Variable biasing differential

ABSTRACT

A variable biasing differential provides an adjustable torque bias between two outputs. An input shaft provides drive torque to a carrier which receives a plurality of stub shafts and a like plurality of planet gears. A first set of planet gears drives a first sun gear and first output and a second set of planet gears, which, in turn, drives additional planet gears which drive a second sun gear and second output. Secured to both ends of the carrier are first and second ring gears which each mesh with an eccentric gear which in turn includes an eccentric second ring gear which meshes with an internal gear disposed about the first and second outputs. These gears are coupled to respective first and second friction clutches which can be independently activated to adjust the torque bias of the differential.

BACKGROUND OF THE INVENTION

The present invention relates generally to motor vehicle differentialsand more particularly to a differential wherein the torque bias betweena pair of outputs may be adjusted.

Geared differentials have been a component of motor vehicle drive trainsfrom the earliest designs. In even the earliest vehicles, it becameapparent that turning a corner and the wheel speed differences createdbetween the inner and outer driving wheels during such maneuvers must beaccommodated by the drive system.

While the standard bevel gear differential has accommodated this wheelspeed difference for decades, improvements have occurred. For example,limited slip differentials which utilize a clutch having a preset torquelimit prevent independent rotation until the forces acting upon thewheels and torque acting upon the axles exceeds a preset value. Thisaddressed a common shortcoming of open differentials which, without sucha feature, would direct drive torque to the tire on the slipperiersurface, thereby frequently causing a vehicle to be trapped or stuckunnecessarily in snow, ice or mud.

Typically differentials are constructed with an equal, i.e., 50-50torque split. This is true whether they are realized in front or rearaxles or as an interaxle or center differential. In a center orinteraxle differential, differentials have also been configured toprovide, for example, a 40-60 torque split or a torque split other than50-50.

The vast majority of active differentials include a mechanism whichtransfers torque from the faster rotating output to the slower rotatingoutput. There are situations where it would be desirable to transfertorque from the slower rotating output to the faster rotating output.Those conditions include when wheel slip initially occurs on the rearwheels when in a corner. When turning, the front wheels are turning at ahigher average speed than the rear. If the biasing mechanism is appliedbefore the average wheel speed of the rear wheels is greater than theaverage speed of the front, the results will be counterproductive. Thetraditional active differential may not have the relative shaft speedsin the proper direction or may have an insignificant relative speeddifference, causing the biasing clutches to be ineffective in creatingthe desired change in vehicle handling or yaw.

The present invention is directed to a differential configurationwherein the torque split between two outputs is adjustable in real time.

SUMMARY OF THE INVENTION

A variable biasing differential provides an adjustable torque biasbetween two outputs. An input shaft provides drive torque to a carrierwhich receives a plurality of stub shafts and a like plurality of planetgears. A first set of planet gears drives a first sun gear and firstoutput and a second set of planet gears, which, in turn, driveadditional planet gears which drive a second sun gear and second output.Secured to both ends of the carrier are first and second ring gearswhich each mesh with an offset gear which in turn includes an offsetsecond ring gear which meshes with an internal gear disposed about thefirst and second output shafts. These gears are coupled to respectivefirst and second friction clutches which can be independently activatedto adjust the torque bias of the differential. A second embodimenthaving a single friction clutch pack is also disclosed.

The torque distribution across a variable biasing differential can havea substantial effect of the vehicle handling by shifting the forcefactors at the tire patch. It can cause the handling of a vehicle toapproach oversteer, understeer or neutral steer in accordance with thedesires of the vehicle manufacturer and vehicle safety considerations. Avariable biasing differential, according to the present invention, candirect drive torque to a desired output under any normal drivingcondition creating a torque balance of, for example, 80-20 to 20-80.This differential can therefore overcome many of the weaknesses found intraditional differentials and active differential systems.

Thus it is an object of the present invention to provide a variablebiasing differential for use on motor vehicles.

It is a further object of the present invention to provide a variablebiasing differential having a planetary gear differential assembly and apair of friction clutch packs.

It is a still further object of the present invention to provide avariable biasing differential for use as either a differential on afront or rear axle or as a center or interaxle differential.

It is a still further object of the present invention to provide avariable biasing differential having a planetary gear differential, apair of offset gear trains and a pair of friction clutches.

Further objects and advantages of the present invention will becomeapparent by reference to the following description of the preferredembodiment and appended drawings wherein like reference numbers refer tothe same component, element or feature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic view of a motor vehicle drive train having avariable biasing differential according to the present inventionutilized as a center or interaxle differential;

FIG. 1B is a diagrammatic view of a motor vehicle drive train having avariable biasing differential according to the present inventiondisposed in a rear axle;

FIG. 2 is a full, sectional view of a first embodiment of a variablebiasing differential according to the present invention;

FIG. 3 is a full, sectional view of a first embodiment of a variablebiasing differential according to the present invention taken along line3-3 of FIG. 2;

FIG. 4 is a full, sectional view of a first embodiment of a variablebiasing differential according to the present invention taken along line4-4 of FIG. 2;

FIG. 5 is a full, sectional view of a first embodiment of a variablebiasing differential according to the present invention taken along line5-5 of FIG. 2;

FIG. 6 is a flat pattern development of a ball ramp operator of a firstembodiment of a variable biasing differential according to the presentinvention taken along line 6-6 of FIG. 2;

FIG. 7 is a full, sectional view of a second embodiment of a variablebiasing differential according to the present invention;

FIG. 8 is a full, sectional view of a second embodiment of a variablebiasing differential according to the present invention taken along line8-8 of FIG. 7; and

FIG. 9 is a flat pattern development of a ball ramp operator of a secondembodiment of a variable biasing differential according to the presentinvention taken along line 9-9 of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS

Referring now to FIG. 1A, a four-wheel vehicle drive train utilizing thepresent invention is diagrammatically illustrated and designated by thereference number 10. The four-wheel vehicle drive train 10 includes aprime mover 12 such as an internal combustion gas or Diesel engine or ahybrid power plant. The prime mover 12 may be either longitudinally ortransversely oriented. The prime mover 12 has an output which is coupledto and directly drives a transmission 14. The output of the transmission14 directly drives a variable biasing differential assembly 16 throughan input shaft 18. The variable biasing differential assembly 16provides drive torque to a primary or rear driveline 20 comprising aprimary or rear prop or output shaft 22, a primary or rear differential24, a pair of live primary or rear axles 26 and a respective pair ofprimary or rear tire and wheel assemblies 28.

The variable biasing differential assembly 16 also provides drive torqueto a secondary or front driveline 30 comprising a secondary or frontprop or output shaft 32 which is disposed concentrically about the inputshaft 18, a secondary or front differential 34, a pair of live secondaryor front axles 36 and a respective pair of secondary or front tire andwheel assemblies 38. Preferably, the front tire and wheel assemblies 38are directly coupled to the respective front axles 36 although manual orremotely activatable locking hubs (not illustrated) may be operablydisposed between the front axles 36 and the respective tire and wheelassemblies 38 to selectively connect same if desired. Finally, both theprimary driveline 20 and the secondary driveline 30 may include suitableand appropriately disposed universal joints 44 which function inconventional fashion to allow static and dynamic offsets andmisalignments between the various shafts and components.

Disposed in sensing relationship with each of the rear tire and wheelassemblies 28 is a wheel speed sensor 48. Preferably, the wheel speedsensors 48 may be the same sensors utilized with, for example, anantilock brake system (ABS) or other vehicle control or traction system.Signals from the sensors 48 are provided in lines 52 to a microprocessor56. Similarly, disposed in sensing relationship with each of the fronttire and wheel assemblies 38 are respective wheel speed sensors 58 whichprovide signals to the microprocessor 56 in the lines 62. Once again,the sensors may be independent or may be part of or shared with anantilock brake system or other vehicle traction control or system.

Frequently, an operator selectable switch 64 or set of push buttons maybe utilized and will be generally disposed within reach of the vehicleoperator in the passenger compartment (not illustrated). The switch 64may be adjusted, for example, to enable or disable the variable biasingdifferential assembly 16. Additionally, a throttle position sensor 66may be utilized to provide a signal to the microprocessor 56 indicativeof the real time position of the throttle or accelerator pedal and asteering angle sensor 68 may similarly provide a signal to themicroprocessor 56 indicative of the real time angular orientation of thefront or primary tire and wheel assemblies 38.

Referring now to FIG. 2, the variable biasing differential assembly 16includes a preferably cast metal housing 98 having various featureswhich receive and support components of the differential assembly 16such as a planetary gear differential assembly 100. The planetary geardifferential assembly 100 is driven by the input shaft 18 which includesa plurality of male or external splines or gear teeth 102 which arecomplementary to and engage internal or female splines or gear teeth 104on a carrier 106. The carrier 106 supports a plurality of stub shafts108, one of which is illustrated in FIG. 2, which each receives one of afirst plurality of planet gears 110 having gear teeth 112 which are inconstant mesh with gear teeth 114 on a first or front sun gear 116integrally formed with or secured to the secondary or front output shaft32.

The planetary gear differential assembly 100 also includes a secondplurality of elongate planet gears 120 which are freely rotatablydisposed upon a like plurality of elongate stub shafts 122 supported byand secured to the carrier 106. Journal bearings or anti-frictionbearings such as needle bearing assemblies 124 may be utilized betweenthe second plurality of elongate planet gears 120 and the elongate stubshafts 122. The second plurality of elongate planet gears 120 includesgear teeth 126 which are complementary to and are in constant mesh withthe gear teeth 112 on the first plurality of planet gears 110. Also inconstant mesh with the teeth 126 on the second plurality of elongateplanet gears 120 are gear teeth 128 on a second or rear sun gear 132integrally formed with or secured to the primary or rear output shaft22.

The input shaft 18 preferably includes a reduced diameter region 136about which is disposed an anti-friction bearing such as a rollerbearing assembly 138. The primary output shaft 22 includes a counterbore or blind aperture 142 which receives the roller bearing assembly138. If desired, flat friction reducing washers 144 may be disposedbetween the various gears 116 and 132 and the central portion of thecarrier 106.

The components of the planetary gear differential assembly 100 justdescribed function as and provide conventional differential actionwhereby the input shaft 18 drives the two output shafts 22 and 32 andthe gearing accommodates a disparity between the rotational speeds ofthe two output shafts 22 and 32.

The variable differential assembly 16 also includes a pair of eccentricgear trains 150A and 150B which are essentially identical but whichoperate in association with the primary or rear output shaft 22 and thesecondary or front output shaft 32, respectively. As such, only one ofthe eccentric gear trains, the gear train 150B, will be described, itbeing understood that the components of the companion gear train 150Aare, for all intents and purposes, the same.

Included in the carrier 106 of the differential assembly 100 is a ringgear 152 having internal or female gear teeth 154 which are in mesh withmale or external gear teeth 156 on an eccentric ring gear 160. Theeccentric ring gear 160 is supported within the housing 98 of thevariable differential assembly 16 for free rotation on an axis offsetfrom the axis of the shafts 18, 22 and 32 by annular bearings such as ajournal bearing 162. Alternatively, the journal bearing 162 may bereplaced with an anti-friction bearing such as a roller bearing assembly(not illustrated). The eccentric ring gear 160 also includes internal orfemale gear teeth 164 which are in constant mesh with male or externalgear teeth 166 formed on a spur gear 170 disposed coaxially with theaxis of the input shaft 18 and the front or secondary output shaft 32.The spur gear 170 includes internal or female splines or gear teeth 172.

The variable biasing differential 100 also includes a pair ofsymmetrically disposed rear and front friction clutch assemblies 180Aand 180B. Once again, since they are the same but for their left andright hand sense, only the rear clutch assembly 180A will be described.For purposes of clarity, however, reference numbers appear in bothassemblies. The friction clutch assembly 180A includes a bell shapedhousing 182 having a smaller diameter cylindrical collar 184 definingmale splines or gear teeth 186 which are complementary to and engage thefemale splines or gear teeth 172 on the spur gear 170. The bell shapedhousing 182 includes internal, axially extending female splines 188which engage a first plurality of complementarily splined largerdiameter main friction clutch plates or disks 190. Interleaved with thefirst plurality of larger diameter main clutch plates or disks 190 are asecond plurality of smaller diameter main clutch plates or disks 192.Clutch paper or other suitable facing material is secured to the facesof the first and second pluralities of main clutch plates or disks 190and 192. The second plurality of smaller diameter main clutch plates ordisks 192 include internal or female splines which are complementary toand engage male or external splines 196 on a circular collar or hub 200.The collar or hub 200 includes female or internal splines or gear teeth202 which engage complementarily configured male or external splines orgear teeth 204 on the primary or rear output shaft 22. The collar or hub200 thus rotates with the primary or rear output shaft 22.

Referring now to FIGS. 2 and 6, the rear friction clutch assembly 180Aalso includes a rear ball ramp operator assembly 210A. The frontfriction clutch assembly 180B likewise includes a front ball rampoperator assembly 210B. Once again, because the ball ramp operatorassemblies 210A and 210B are identical except for their mirror imagedisposition, only the rear ball ramp operator 210A will be described,although for reasons of clarity, reference numbers may appear in eitherassembly. The rear ball ramp operator assembly 210A includes a first orprimary circular apply plate 212 having a plurality of arcuate recesses214 which receive a like plurality of load transferring balls 216. Thefirst circular apply plate 212 includes internal or female spines orgear teeth 218 which are complementary to the male or external splinesor gear teeth 196 on the collar or hub 200. Accordingly, the firstcircular apply plate 212 rotates with the collar or hub 200.

Disposed adjacent the first circular apply plate 212 is a smallerdiameter circular member 222. The smaller diameter circular member 222includes a like plurality of arcuate recesses 224 which also receive theload transferring balls 216. It will be appreciated that the pluralityof ramped recesses 214 and 224 and the load transferring balls 216 maybe replaced with other analogous mechanical elements which cause axialdisplacement of the apply plate 212 and the circular member 222 inresponse to relative rotation therebetween. For example, tapered rollersdisposed in complementarily configured conical helices or opposed camshaving complementary multiple oblique surfaces may be utilized.

The smaller diameter circular member 222 defines external or malesplines 228 which receive and drive a first plurality of smallerdiameter pilot clutch plates or disks 232 having internal or femalesplines. Interleaved with the first plurality of pilot clutch plates ordisks 232 is a second plurality of larger diameter pilot clutch platesor disks 234 having external or male splines which are complementary toand engage the splines 188 on the interior surface of the bell shapedhousing 182. Accordingly, the second plurality of pilot clutch plates ordisks 234 rotates therewith.

A circular plate or thick flat washer 236 includes male or externalsplines 238 which engage the splines 188 on the bell shaped housing 182and it thus rotates therewith. Preferably, a thin thrust washer 240 isdisposed between the flat washer 236 and first circular apply plate 212and reduces friction therebetween. A thrust bearing 242 is disposedadjacent the smaller circular member 222 and is retained in position onthe collar or hub 200 by a snap ring 244 which seats within acomplementarily configured circumferential channel or groove 246 formedin the collar or hub 200. An axially moving actuator plate 250 engages athrust bearing 252 and a second circular apply plate 254 which istranslated axially toward the clutch pack assemblies 180 by an actuatorrod 256 which in turn is axially, bidirectionally translated by abidirectional electric actuator 260. The bidirectional actuator 260 isunder the control of the microprocessor 56 illustrated in FIG. 1A.

The operation of the variable biasing differential assembly 16 will nowbe described with reference to FIG. 2. As noted above, it will beappreciated that the input shaft 18 and the planetary gear differentialassembly 100 including the carrier 106, the planet gears 110 and 120,the front sun gear 116 and the rear sun gear 132 as well as therespective associated output shafts 32 and 22 operate as a conventionalplanetary gear differential disposed in the center of the vehicle, aconfiguration often referred to as a center differential.

With regard to the planetary gear differential assembly 100, it shouldbe noted that the diameters of the sun gears 116 and 132, asillustrated, are not equal. The rear sun gear 132 is larger than thefront sun gear 116 so that the meshing elongate planetary gears 120 willnot interfere with the rotation of the front sun gear 116. Thisdifference in diameters results in a differential ratio dependent uponthe relative diameters but which will never be closer to being equalthan a 48:52 ratio. This ratio, when the differential assembly 100 is inan unbiased state, is considered to be equal. This ratio, however, maybe increased if desired by adjusting the relative diameters of the sungears 116 and 132.

Driven by the carrier 106 are the respective front and rear offset oreccentric ring gears 160. These drive the spur gears 170 and theassociated, respective bell housings 182 at a speed which is slightlyslower than the non-differentiated speed of the respective output shafts18 and 22. When the electric actuator 260 translates the shift rod 256either to the left or to the right to engage the friction clutch packs180A or 180B, compression of the main clutch plates or discs 190 and 192by the associated primary circular apply plate 212 transmits a torquefrom the associated rear or front output shaft 22 or 18 to the clutchhousing 182 which is reflected back through the eccentric gearing andthe planetary gear differential assembly 100 to the other output shaft18 or 22.

Thus, the differential is capable of transferring torque from a slowerrotating output to a faster rotating shaft. This configuration alsoreduces the torque transmitted through the main clutch plates 190 and192 and reduces the speed differences at the friction surfaces. Thereduced torque and reduced speed both contribute to reducing the heatproduced in the clutches and thus enhances the life of the clutches andthe differential assembly 16.

It should be noted that the friction clutch assemblies 180A and 180B areand are intended to be slipping clutches as opposed to locking clutchesand do not and are not intended to operate in a locked mode which wouldtypically result in a 20% speed overrun of one output over the other.

It should also be noted that while other, including single and dualelectric, pneumatic or hydraulic actuators or operators of diversedesigns may be utilized in place of the single electric actuator 260, asingle actuator provides all necessary operational action as there isnever need nor reason to apply both clutch assemblies 180A and 180Bsimultaneously.

Referring now to FIG. 1B, a four wheel vehicle drivetrain utilizing thepresent invention in a rear axle is diagrammatically illustrated anddesignated by the reference number 70. The four wheel vehicle drivetrain70 includes a prime mover 12 such as an internal combustion or Dieselengine. The prime mover 12 may be either longitudinally or transverselyoriented. The prime mover 12 has an output which is coupled to anddirectly drives a transaxle 74. A first output of the transaxle 74directly drives an alternate embodiment variable biasing reardifferential assembly 80 through a prop shaft 82. The variable biasingrear differential assembly 80 provides drive torque to a pair of liverear axles or shafts 26A and 26B and a respective pair of rear tire andwheel assemblies 28.

The transaxle 74 also provides drive torque to a pair of live frontaxles 36′ and a respective pair of front tire and wheel assemblies 38.Finally, the prop shaft 82 may include suitable and appropriatelydisposed universal joints 84 which accommodate static and dynamicoffsets and misalignments between the prop shaft 82 and associatedcomponents.

Disposed in sensing relationship with each of the rear tire and wheelassemblies 28 is a rear wheel speed sensor 48. The wheel speed sensors48 may be independent or may be the same sensors utilized with, forexample, an antilock brake system (ABS) or other vehicle tractioncontrol or stability system. Signals from the sensors 48 are provided inlines 52 to a microprocessor 56. Similarly, disposed in sensingrelationship with each of the front tire and wheel assemblies 38 arerespective front wheel speed sensors 58 which provide signals to themicroprocessor 56 in the lines 62. Once again, the sensors 58 may beindependent or may be part of or shared with an antilock brake system orother vehicle traction control or stability system.

Optionally, an operator selectable switch 64 or set of push buttons maybe utilized and will be generally disposed within reach of the vehicleoperator in the passenger compartment (not illustrated). The switch 64may be adjusted, for example, to enable or disable the variable biasingdifferential assembly 16. Additionally, a throttle position sensor 66may be utilized to provide a signal to the microprocessor 56 indicativeof the real time position of the throttle or accelerator pedal and asteering angle sensor 68 may similarly provide a signal to themicroprocessor 56 indicative of the real time angular orientation of thefront tire and wheel assemblies 38.

Referring now to FIGS. 1B and 7, the second embodiment variable biasingdifferential 80 includes a first, smaller bevel gear 276 which drives asecond, larger bevel gear 278 which are both received within acylindrical housing 280. A cylindrical extension 282 of the larger bevelgear 278 is supported in the housing 280 within a journal oranti-friction bearing assembly 284. Additionally, the extension 282 ofthe larger bevel gear 278 is supported by a tapered roller bearingassembly 286 which in turn is supported by the left rear axle 26A. Thecylindrical extension 282 of the larger bevel gear 278 includes internalor female splines or gear teeth 288.

Referring now to FIGS. 7 and 8, the second embodiment variable biasingdifferential assembly 80 also includes a planetary gear differentialassembly 290. The planetary gear differential assembly 290 includes acarrier 292 includes a reduced diameter portion having external or malesplines or gear teeth 294 which mate within and are complementary to theinternal or female splines or gear teeth 288 on the larger bevel gear278. The reduced diameter portion of the carrier 292 is freely rotatablysupported upon the left rear axle 26A by a roller bearing assembly 296.Secured to the carrier 292 for rotation therewith are a first pluralityof stub shafts 302, one of which is illustrated in FIG. 7. Each of thefirst plurality of stub shafts 302 supports an anti-friction rollerbearing assembly 304 which, in turn, freely rotatably supports a planetgear 306. The planet gears 306 include exterior male gear teeth 308which are complementary to and in constant mesh with gear teeth 312 on afirst or right side sun gear 314. The first or right side sun gear 314includes female or internal splines or gear teeth 316 which arecomplementary to and mate with external or male splines or gear teeth318 formed on an end adjacent portion of the right rear axle 26B.

Also driven by the first plurality of planet gears 306 is a secondplurality of planet gears 324 having a first, smaller diameter set ofgear teeth 326 and a second, larger diameter set of gear teeth 328. Thesecond plurality of planet gears 324 are rotatably disposed uponanti-friction roller bearing assemblies 332 which in turn are supportedby a plurality of stub shafts 334 which are received within and securedto the carrier 292. The larger diameter gear teeth 328 of the secondplurality of planet gears 324 are in constant mesh with gear teeth 336on a second or left side sun gear 338. The second or left side sun gear338 includes internal or female splines or gear teeth 342 which arecomplementary to and mate with exterior or male splines or gear teeth344 on the left rear axle 26A. A roller bearing assembly 346 which isreceived within a counter bore 348 of the left rear axle 26A rotatablysupports and stabilizes the rear axles 26A and 26B relative to oneanother. A flat washer 352 disposed between the first sun gear 314 andthe second sun gear 338 reduces friction therebetween and maintainsthese gears in their proper axial positions. It will be appreciated thatthe planetary gear differential 290 just described operates as aconventional differential to accommodate speed differences between therear axles 26A and 26B when, for example, an associated vehicle turns acorner.

Referring again to FIG. 7, the second embodiment rear variable biasingdifferential assembly 80 also includes a differential drive assembly360. The differential drive assembly 360 includes a U-shaped housing 362having longitudinal exterior grooves 364 which are engageable byradially disposed stops or pins 366 to maintain the housing 362stationary within the differential assembly 80. The radial pins 366 maybe secured and stabilized by suitable components such as acircumferential ring 368 and a snap ring 372.

Preferably disposed at 120° intervals within the stationary housing 362are three stub shafts 374, one of which is illustrated in FIG. 7. Thestub shafts 374 are secured to the stationary housing 362 and are thusalso stationary. The three stub shafts 374 support roller bearingassemblies 376 which, in turn, freely rotatably support three dualdiameter gears 380. The dual diameter gears 380 include a first, largerdiameter set of external or male gear teeth 382 which are complementaryto and in constant mesh with internal or female gear teeth 384 on afirst collar 386 which is secured to and rotates with the carrier 292 ofthe planetary gear differential assembly 290. The three dual diametergears 380 also include sets of smaller diameter external or male gearteeth 392 complementary to and in constant mesh with internal or femalegear teeth 394 on a second cylindrical collar 396. The secondcylindrical collar 396 includes internal or female splines or gear teeth398.

The variable biasing rear differential assembly 80 also includes a ballramp clutch assembly 400. The ball ramp clutch assembly 400 includes abell shaped housing 402 having a smaller diameter hub region 404 whichis freely rotatably disposed about the right axle 26B upon a journal oranti-friction bearing assembly 406. A thrust bearing 408 maintains theaxial position of the housing 402 relative to the right axle or shaft26B and the axial position of the thrust bearing 408 and an adjacentflat washer 412 is maintained by a snap ring 414 which is receivedwithin a suitable circumferential groove 416 in the right axle or shaft26B.

The housing 402 includes a larger diameter portion 422 having externalor male splines or gear teeth 424 which are complementary to and engagethe female splines 398 on the second cylindrical collar 396. Thus, thehousing 402 rotates with the second cylindrical collar 396. On theinterior surface of the larger diameter portion 422 of the housing 402are a plurality of longitudinally extending internal or female splinesor gear teeth 426. The plurality of internal splines or gear teeth 426are engaged by complementarily configured splines on a first pluralityof larger diameter main friction clutch plates or discs 428. Interleavedwith the first plurality of larger diameter main clutch plates or discs428 are a second plurality of smaller diameter main clutch plates ordiscs 432. Both the first and second pluralities of main clutch platesor discs 428 and 432 include suitable clutch paper or facing material aswill be readily appreciated.

The smaller diameter friction clutch plates or discs 432 include splineswhich are engaged by external splines 434 on a clutch hub or collar 436.In turn, the clutch collar 436 is splined by an interengaging set ofsplines 438 to the right rear axle or shaft 26B. A circular apply plate442 also includes internal or female splines 444 which engage the malesplines 434 on the clutch collar 436. Thus, the circular apply plate 442rotates with the clutch collar 436 and the right rear axle or shaft 26B.As illustrated in FIGS. 7 and 9, the circular apply plate 442 includes aplurality of spaced apart arcuate recesses 446 which each receive one ofa like plurality of load transferring balls 448. Typically andpreferably three arcuate recesses 446, spaced at 120° intervals, will beutilized. A circular member 452 includes a like plurality of similarlyspaced apart recesses 454 which likewise receive and trap the loadtransferring balls 448. It will be appreciated that the plurality oframped recesses 446 and 454 and the load transferring balls 448 may bereplaced with other analogous mechanical elements which cause axialdisplacement of the circular apply plate 442 and the circular member 452in response to relative rotation therebetween. For example, taperedrollers disposed in complementarily configured conical helices oropposed cams having complementary multiple oblique surfaces may beutilized.

The circular member 452 includes male or external splines 456 which areengaged by a first plurality of smaller diameter pilot clutch plates ordiscs 458. Interleaved with the first plurality of smaller diameterpilot clutch plates or discs 458 is a second plurality of largerdiameter pilot clutch plates or discs 462. The larger diameter pilotclutch plates or discs 462 engage the splines 426 on the housing 402 andthus rotate therewith. Both the smaller and larger diameter pilot clutchplates 458 and 462 include suitable clutch paper or facing material aswill be readily appreciated. The axial position of the circular member454 is maintained by a thrust bearing 466 which abuts a shoulder 468 inthe right rear axle 26B.

The variable biasing rear differential assembly 80 also includes anactuator assembly 470. The actuator assembly 470 includes abidirectional, fractional horsepower electric motor 472 whichbi-directionally drives a pinion gear 474. The pinion gear 474 engagesperipheral external gear teeth 476 on a ring gear 478 having internal orfemale threads 482. The internal threads 482 are complementary to andengage external or male threads 484 on a stationary ring member 486. Asthe pinion 474 bi-directionally rotates, the ring gear 478 likewiserotates and translates axially at greatly reduced speed and withincreased torque. The ring gear 478 engages a circular washer or spacer492 which, in turn, engages a generally circular, obliquely extendingtransfer member 494 which engages and compresses the first and secondpilot clutch plates 458 and 462.

The variable biasing rear differential assembly 80 also includes alubrication pump 500 which provides a flow of lubricating fluid to anaxial passageway 502 in the right axle 26B. A plurality of radial ports504 distribute the fluid to the various components of the differentialassembly 80. A fluid tight seal 506 closes off the open end of the axialpassageway 502. An anti-friction bearing such as a ball bearing assembly508 rotatably supports the right rear axle 26B within the housing 280and an oil seal 510 provides a suitable fluid impervious sealtherebetween.

Operation of the second embodiment variable biasing differentialassembly 80 will now be described with reference to FIG. 7. As notedabove, the planetary gear differential assembly 290 operates as aconventional differential assembly to permit disparate rotational speedsbetween the rear axles 26A and 26B while providing drive torque theretofrom the larger diameter bevel gear 278. Because of the distinctdiameters of the gears 326 and 328 within the differential assembly 290,there will be an unequal torque split which will transfer or pre-biasthe torque to, for example, the rear wheels of a rear wheel drivevehicle such that they receive 60% of the drive torque and the frontwheels receive 40% of the drive torque.

The operation of the second embodiment variable biasing differentialassembly 80 is similar to the first embodiment variable biasingdifferential assembly 16 in that because of the speed reduction achievedthrough the differential drive assembly 360, the output of thedifferential drive assembly 360 and specifically the bell-shaped housing422 of the friction clutch pack assembly 400 will be turning at a slowerspeed than the carrier 292. Accordingly, when the friction clutch packassembly 400 is activated by energization of the bidirectional electricmotor 472, torque is reflected through the friction clutch pack assembly400 from the right output shaft 26B, through the differential gear train360 and into the left output shaft 26A. Whereas bias initially might be60% to the shaft 26B and 40% to the shaft 26A, activation of thefriction clutch pack 400 can deliver 80% torque to the left axle 26A and20% torque to the right axle 26B.

In the foregoing descriptions, the first embodiment variable biasingdifferential assembly 16 is illustrated and described as a center orinteraxle differential whereas the second embodiment variable biasingdifferential assembly 80 is illustrated and described as a reardifferential. It should be appreciated that inasmuch as bothdifferential assemblies 16 and 80 may be set to deliver equal torque orinitial pre-bias in one direction, i.e., significantly more torquedelivered to the rear axle in normal operating conditions and thenactivated to deliver significantly more torque to the front of thevehicle, both differential assemblies 16 and 80 are suitable forinstallation in either the center differential or rear axle locationillustrated in FIGS. 1A and 1B, respectively.

The foregoing disclosure is the best mode devised by the inventor forpracticing this invention. It is apparent however, that devicesincorporating modifications and variations will be obvious to oneskilled in the art of motor vehicle differentials. Inasmuch as theforegoing disclosure presents the best mode contemplated by the inventorfor carrying out the invention and is intended to enable any personskilled in the pertinent art to practice this invention, it should notbe construed to be limited thereby but should be construed to includesuch aforementioned obvious variations and be limited only by the spiritand scope of the following claims.

1-20. (canceled)
 21. A variable biasing differential for a motor vehicledriveline comprising, in combination, a drive member, a first drivenmember, a second driven member, a differential having a housing drivenby said drive member and driving said first driven member and saidsecond driven member, a speed reducing gear train having an input drivenby said differential housing and an output, a friction clutch having afirst clutch feature coupled to said output of said gear train and asecond clutch feature coupled to one of said driven members, and anactuator for selectively engaging said friction clutch.
 22. The variablebiasing differential of claim 21 wherein said variable biasingdifferential is utilized as a center differential.
 23. The variablebiasing differential of claim 21 wherein said variable biasingdifferential is utilized as a rear axle differential.
 24. The variablebiasing differential of claim 1 further including a second speedreducing gear train and a second friction clutch.
 25. The variablebiasing differential of claim 21 wherein said gear train includes aplurality of gears having a portion of larger diameter and a portion ofsmaller diameter, said portion of larger diameter driven by said housingand said portion of smaller diameter operably driving said first clutchfeature.
 26. The variable biasing differential of claim 21 wherein saidactuator includes a ball ramp operator and a pilot friction clutch pack.27. The variable biasing differential of claim 21 wherein said geartrain includes an eccentric gear disposed intermediate said housing andsaid friction clutch.
 28. A variable biasing differential for a vehicledrive train comprising, in combination, a drive member, a first drivenmember disposed on an axis, a second driven member disposed on saidaxis, a differential having a housing driven by said drive member anddriving said first driven member and said second driven member, a firsteccentric gear train driven by said housing and having a first reducedspeed output, a first friction clutch having a first clutch componentcoupled to said first driven member and a second clutch componentoperably coupled to said first reduced speed output of said firsteccentric gear train, a second eccentric gear train driven by saidhousing and having a second reduced speed output, a second frictionclutch having a third component coupled to said second driven member anda fourth clutch component operably coupled to said second reduced speedoutput of said second eccentric gear train, and an actuator forindependently engaging said first and said second friction clutches. 29.The variable biasing differential of claim 8 wherein said variablebiasing differential is disposed in said drive train as a centerdifferential.
 30. The variable biasing differential of claim 8 whereinsaid variable biasing differential is disposed in said drive train as arear axle differential.
 31. The variable biasing differential of claim28 wherein said first output member is coupled to a front prop shaft andsaid second output member is coupled to a rear prop shaft.
 32. Thevariable biasing differential of claim 28 wherein said actuator includesa ball ramp mechanism having a pair of adjacent members defining arcuaterecesses and load transferring members disposed in said recesses. 33.The variable biasing differential of claim 28 wherein said actuator iselectric and has a linear, bidirectional output.
 34. The variablebiasing differential of claim 38 wherein said actuator includes a ballramp operator and pilot friction clutch pack.
 35. A variable biasingdifferential comprising, in combination, a drive member disposed on anaxis, a first driven member disposed on said axis, a second drivenmember disposed on said axis, a geared differential having a housingdriven by said drive member and driving said first driven member andsaid second driven member, a gear train driven by said housing having areduced speed output, a friction clutch having a first clutch membercoupled to one of said driven members and a second clutch member coupledto said reduced speed output of said gear train, an actuator forselectively applying engagement force to said friction clutch.
 36. Thevariable biasing differential of claim 35 wherein said variable biasingdifferential is disposed as a center differential.
 37. The variablebiasing differential of claim 35 wherein said variable biasingdifferential is disposed as a rear axle differential.
 38. The variablebiasing differential of claim 35 wherein said actuator includes a ballramp actuator, a pilot friction clutch and bi-directionally translatingmeans for engaging said friction clutch.
 39. The variable biasingdifferential of claim 35 wherein said gear train includes a plurality ofgears having a portion of larger diameter and a portion of smallerdiameter, said portion of larger diameter driven by said carrier andsaid portion of smaller diameter driving said first plurality of clutchplates.
 40. The variable biasing differential of claim 35 wherein saidactuator includes an electric motor, a threaded ring gear driven by saidelectric motor, whereby said ring gear translates axially in response torotation of said electric motor.